fix(telemetry): validate activity state shape

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/posthog-activity-state.test.ts

@@ -0,0 +1,122 @@
+import { afterEach, describe, expect, it } from "bun:test"
+import { mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { tmpdir } from "node:os"
+
+const originalXdgDataHome = process.env.XDG_DATA_HOME
+
+function createDataHomePath(): string {
+  return join(tmpdir(), `posthog-activity-state-${Date.now()}-${Math.random()}`)
+}
+
+async function importPostHogActivityStateModule(): Promise<typeof import("./posthog-activity-state")> {
+  return import(`./posthog-activity-state?test=${Date.now()}-${Math.random()}`)
+}
+
+afterEach(() => {
+  if (originalXdgDataHome === undefined) {
+    delete process.env.XDG_DATA_HOME
+  } else {
+    process.env.XDG_DATA_HOME = originalXdgDataHome
+  }
+})
+
+describe("getPostHogActivityCaptureState", () => {
+  it("returns default state when activity file contains null", async () => {
+    // given
+    const dataHomePath = createDataHomePath()
+    const cachePath = join(dataHomePath, "oh-my-opencode")
+    mkdirSync(cachePath, { recursive: true })
+    writeFileSync(join(cachePath, "posthog-activity.json"), "null\n")
+    process.env.XDG_DATA_HOME = dataHomePath
+    const { getPostHogActivityCaptureState } = await importPostHogActivityStateModule()
+
+    // when
+    const result = getPostHogActivityCaptureState(new Date("2026-04-11T10:15:00.000Z"))
+
+    // then
+    expect(result).toEqual({
+      dayUTC: "2026-04-11",
+      hourUTC: "2026-04-11T10",
+      captureDaily: true,
+      captureHourly: true,
+    })
+
+    rmSync(dataHomePath, { recursive: true, force: true })
+  })
+
+  it("returns default state when activity file contains an array", async () => {
+    // given
+    const dataHomePath = createDataHomePath()
+    const cachePath = join(dataHomePath, "oh-my-opencode")
+    mkdirSync(cachePath, { recursive: true })
+    writeFileSync(join(cachePath, "posthog-activity.json"), "[]\n")
+    process.env.XDG_DATA_HOME = dataHomePath
+    const { getPostHogActivityCaptureState } = await importPostHogActivityStateModule()
+
+    // when
+    const result = getPostHogActivityCaptureState(new Date("2026-04-11T10:15:00.000Z"))
+
+    // then
+    expect(result).toEqual({
+      dayUTC: "2026-04-11",
+      hourUTC: "2026-04-11T10",
+      captureDaily: true,
+      captureHourly: true,
+    })
+
+    rmSync(dataHomePath, { recursive: true, force: true })
+  })
+
+  it("returns default state when activity file contains a number", async () => {
+    // given
+    const dataHomePath = createDataHomePath()
+    const cachePath = join(dataHomePath, "oh-my-opencode")
+    mkdirSync(cachePath, { recursive: true })
+    writeFileSync(join(cachePath, "posthog-activity.json"), "42\n")
+    process.env.XDG_DATA_HOME = dataHomePath
+    const { getPostHogActivityCaptureState } = await importPostHogActivityStateModule()
+
+    // when
+    const result = getPostHogActivityCaptureState(new Date("2026-04-11T10:15:00.000Z"))
+
+    // then
+    expect(result).toEqual({
+      dayUTC: "2026-04-11",
+      hourUTC: "2026-04-11T10",
+      captureDaily: true,
+      captureHourly: true,
+    })
+
+    rmSync(dataHomePath, { recursive: true, force: true })
+  })
+
+  it("reads valid activity state JSON", async () => {
+    // given
+    const dataHomePath = createDataHomePath()
+    const cachePath = join(dataHomePath, "oh-my-opencode")
+    mkdirSync(cachePath, { recursive: true })
+    writeFileSync(
+      join(cachePath, "posthog-activity.json"),
+      `${JSON.stringify({
+        lastActiveDayUTC: "2026-04-11",
+        lastActiveHourUTC: "2026-04-11T10",
+      })}\n`,
+    )
+    process.env.XDG_DATA_HOME = dataHomePath
+    const { getPostHogActivityCaptureState } = await importPostHogActivityStateModule()
+
+    // when
+    const result = getPostHogActivityCaptureState(new Date("2026-04-11T10:15:00.000Z"))
+
+    // then
+    expect(result).toEqual({
+      dayUTC: "2026-04-11",
+      hourUTC: "2026-04-11T10",
+      captureDaily: false,
+      captureHourly: false,
+    })
+
+    rmSync(dataHomePath, { recursive: true, force: true })
+  })
+})

src/shared/posthog-activity-state.ts

@@ -32,6 +32,10 @@ function getUtcHourString(date: Date): string {
   return date.toISOString().slice(0, 13)
 }
 
+function isPostHogActivityState(value: unknown): value is PostHogActivityState {
+  return value !== null && typeof value === "object" && !Array.isArray(value)
+}
+
 function readPostHogActivityState(): PostHogActivityState {
   const stateFilePath = getPostHogActivityStateFilePath()
   if (!existsSync(stateFilePath)) {
@@ -40,7 +44,10 @@ function readPostHogActivityState(): PostHogActivityState {
 
   try {
     const content = readFileSync(stateFilePath, "utf-8")
-    const parsed = JSON.parse(content) as PostHogActivityState
+    const parsed: unknown = JSON.parse(content)
+    if (!isPostHogActivityState(parsed)) {
+      return {}
+    }
     return parsed
   } catch (error) {
     log("[posthog-activity-state] Failed to read activity state", {